It is necessary to handle electrical components for a variety of purposes in modern technology. One major area in which many components have to be handled is the application of components to substrates, for example printed circuit boards, in the assembly of electronic circuitry. In the handling of electronic components, specially in placing various components on printed circuit boards, it is essential that the components be positioned precisely at a desired location and in a desired orientation. Many machines have been proposed for accurately placing components on substrates. Some of these previously known machines have included so-called pick-up heads by which components are picked up from a component supply and placed in a desired position and orientation on a suitable substrate. U.S. Pat. Nos. 4,135,630 and 4,290,732 both describe machines for picking up electrical components and placing them at desired positions and orientations on a suitable substrate. The pick-up heads of the machines described in each of these U.S. patent specifications have a vacuum or suction tool by which components are held on the pick-up head and so-called pawls or fingers by which the components are positioned accurately in correct orientation on the tool. Machines of this type are capable of very precise positioning of components of appropriate size. However, it is frequently necessary to position a number of components of widely varying sizes on a single substrate. By way of example components to be placed on a single board may have sides ranging from 1.25 mm to 31.5 mm in length and may be up to 6.5 mm in thickness. The heretofore known machines, for example of the type described in the aforementioned U.S. patent specifications, are capable of satisfactorily handling a small range of sizes of components; however, in order to accommodate components of the size variation which it is often necessary to position on substrates, sufficient accuracy and reliability has not been achieved with a single pick-up head without manually adjusting or changing the pawls or fingers, or alternatively providing the components in an already orientated manner. This latter system demands extreme accuracy in delivering components to the pick-up head which requires a component feed means which is dimensionally accurate to very close tolerances and hence which is very expensive--known component feed systems provide components in pockets of reeled tapes or so-called "sticks" in both of which cases it is difficult to ensure that the components supplied are oriented in the component supply sufficiently accurately. In addition, if, in order to achieve sufficiently precise positioning, the component feed is relied on to give the necessary accuracy, there is a considerable period (from picking the components from the component supply to finally placing the components on the substrata) during which the components may be disturbed on the pick-up head thereby losing the orientation and precise positioning of the components. Changing of the pawls or fingers on pick-up heads of the type shown in the aforementioned U.S. patent specifications would be a most inconvenient and time-consuming operation and, furthermore, it is difficult to ensure that the replacement pawls or fingers are sufficiently precisely mounted on the pick-up head--great care is required to achieve the necessary precision. Accordingly, where components of a wide variety of dimensions have been called for on a single substrate it has been customary to present the substrate to a plurality of pick-up heads each capable of handling components of different and complementary size ranges. Precision pick-up heads are expensive and a plurality of heads is, furthermore, wasteful of space.